1. Field of the Invention
The present invention relates to the field of wireless communications, and more particularly to patch antennas.
2. Description of Related Art
Wireless devices have become an integral life style among mobile professionals and consumers worldwide. Users of wireless devices demand a more compact, yet powerful cellular phones, mobile devices, and personal digital assistants (PDAs). One approach to reduce the overall size of a wireless device is to reduce the dimension of a patch antenna. FIG. 1 illustrates a conventional patch antenna 10 having a first slot 11 and a second slot 13 interconnected with each other by a full transmission line 12. The first slot 11 and the second slot 13 operate as the two primary radiators in the mechanism of the patch antenna 10. The full transmission line 12, typically implemented as a half wavelength, is placed between the first slot 11 and the second slot 13, ensuring that the first slot 11 and the second slot 13 will be fed by a xcexg/2 decay in order to extract the maximum efficiency from the patch antenna structure 10.
An equivalent circuit 20 representing the patch antenna 10 is shown in FIG. 2. The equivalent circuit 20 is constructed with capacitors 21 and 22, resistors 23 and 24, and inductors 25 and 26. The capacitors 21 and 22 denote the fringing capacitance, the resistors 23 and 24 denoting the radiative resistance, and the elements 25 and 26 denoting a decay representing a transmission line.
A typical delay of xcexg/2 is often necessary to attain maximum efficiency. A way to reduce the dimension of a patch is to make decay in less space by a fictive xcexg/2. One conventional approach to increase the amount of delay in a given space of a transmission line is by loading the transmission line either capacitively or inductively, as described, for example, in S. Reed, L. Desclos, C. Terret, S. Toutain, xe2x80x9cPatch Antenna Size Reduction by Inductive Loadingxe2x80x9d, in Microwave Optical Technology Letters April 2001.
Accordingly, it is desirable to have structures and methods of an antenna that is compact in size while attaining maximum efficiency.
The invention discloses a full transmission line replaced by a set of transmission lines connected between two slots or radiative elements. Components can be inserted in the space between the transmission lines. In an alternative embodiment, the transmission fines are cranked or bended for a more compact dimension of transmission lines. The cranked or bended transmission lines can also be loaded by inductive elements. In another embodiment, a patch antenna is constructed with n sets of transmission lines between the two slots, where each set of transmission line produces a different electrical length in accordance with a particular frequency. In a further embodiment, a set of intermediate filters is added within the transmission lines for differentiating the frequencies. The function of a filter is to pass through a predetermined frequency but rejecting other frequencies, which potentially can destroy the radiation effect.
Advantageously, the present invention reduces the overall dimension of a patch antenna, thereby decreases the overall size of a wireless device. Other structures and methods are disclosed in the detailed description below. This summary does not purport to define the invention. The invention is defined by the claims.